Technical Field
The present application relates to an internal combustion engine, and more particularly, to an internal combustion engine comprising a bottom surface of a cylinder head on which a heat shield film is formed.
Background Art
JP 2010-249008 A discloses an art to form an anodizing film on a wall surface of a combustion chamber of an internal combustion engine. The anodizing film has lower thermal conductivity than a metal base material consisting of the combustion chamber (e.g. aluminum alloy, magnesium ally, titanium alloy). Therefore, when the anodizing film is formed on the wall surface, thermal shield performance of the combustion chamber is improved and also cooling loss of the combustion chamber is reduced. Such art is also disclosed in JP 2012-072749 A.
In a gasoline type internal combustion engine, there is an engine with the cylinder head to which a fuel injector (hereinafter referred to as a “cylinder injector”) is mounted. In addition to the cylinder injector, some engine comprise a sensor to detect pressure in the combustion chamber (hereinafter referred to as a “cylinder pressure sensor”). In a diesel type internal combustion engine, there is an engine with the cylinder head to which a glow plug combined with the cylinder pressure sensor is mounted.
For the mounting of the cylinder injector or the cylinder pressure sensor, an exclusive installation hole is generally formed in the cylinder head. In such case, however, fuel not contributing to combustion (hereinafter referred to as “unburnt HC”) easily occurs in the combustion chamber. The reasons are that combustion gas tends to lose its momentum to go off around an opening portion of the installation hole at the combustion chamber side and thus temperature of the opening portion easily goes down. Since unburned HC leads to deterioration of thermal efficiency of the internal combustion engine, it is desirable to suppress occurrence of unburned HC.
Unburned HC is sometimes thermally decomposed into gummy matter (hereinafter referred to as “deposit”). Moreover, the accumulation of deposit on the opening portion may increase risk of developing various troubles. That is, in case of the cylinder injector, shape of fuel injected therefrom (i.e. spray shape of the injected fuel) might change from the original form, and/or flow mass of fuel supplied to the combustion chamber might decrease from the estimated flow mass. In case of the cylinder pressure sensor, an output error thereof might become large. In addition to that, when deposit falls from the opening portion, the fallen deposit might induce abnormal combustion. Even from such a point of view, it is desirable to suppress occurrence of unburned HC.
However, JP 2010-249008 A or JP 2012-072749 A mentions mainly about the heat shield film like the anodized film formed on the bottom surface of the cylinder head which occupies a part of the wall surface of the combustion chamber whereas being silent to the view in suppressing occurrence of unburned HC in the combustion chamber.